Perforations in continuous material are required in a variety of manufacturing processes. In particular, adhesive bandages are uncomfortable to the bandage user unless there are perforations through the bandages to allow access to some ambient air, called "breathing". The number of perforations in the material, as well as the diameter of each perforation in the material, contribute to the air flow rate through material in cubic feet per minute per square foot. This air flow rate is referred to as porosity. Initially, mechanical punches were used to perforate the web of materials for adhesive bandages. Mechanical punches are limited to slower web speeds. Additionally, these punches required a great deal of maintenance for operation. The most crucial problem with the mechanical punches is the risk that the pins of the punches would break and lodge in the web, possibly injuring the bandage user.
Hot pin perforation is also known in the prior art. The limitations of hot pin perforation are numerous, including slow web speed, poor (non-circular) hole formation with raised rings of melted material around each hole, rough texture of the web due to the raised rings and the inefficient application of heat to the entire surface of the material. The results of hot pin perforations are marginal when foam is employed in the web.
Ultrasonic perforation is also employed in the prior art. The prior art ultrasonic systems employ ultrasonic equipment adjacent to a pin roll with a fixed gap of space in the path of the web between the ultrasonic equipment and the pin roll. This gap is created by the placement of a stop that limits movement of the ultrasonic equipment toward the pin roll. This fixed gap results in changes in the perforations over time due to the fact that the gap changes when the ultrasonic equipment is heated by use, and yields higher porosity as the temperature of the ultrasonic horn increases. The prior art also requires precise machining of the pin roll to an exact concentricity to avoid changes in the gap, and thus in the perforations, due to unevenness in the pin roll, and the repeated calibration of the ultrasonic equipment's position relative to the pin roll to maintain the fixed gap and thereby avoid changes in the perforations.
Thus, there exists a need for a web perforation system that offers high speeds, improved perforation quality control, and lower risk of injury to the ultimate user.